1. Field of the Invention
The present invention relates in general to control systems for controlling internal combustion engines of a variable valve type wherein open/close movements of the intake and exhaust valves are controlled in accordance with an operation condition of the engine, and more particularly to the control systems of a type that controls the intake air amount by controlling the close timing (viz., open period) of each intake valve to carry out a so-called non-throttle operation of the engine. More specifically, the present invention is concerned with the control systems of a type that allows the engine to work under various operation cycles.
2. Description of the Prior Art
Nowadays, variable valve type internal combustion engines are widely employed in motor vehicles for the superiority of the engine. In fact, fuel consumption and driveability under lower speed and low load engine operation are improved and at the same time due to increased mixture charging effect, sufficient output under high speed and high load engine operation is obtained.
For controlling such engines, Laid-open Japanese Patent Application (viz., Tokkaihei) 8-200025 shows a control system. The variable valves of this publication are actuated by electromagnetic actuators, and the open/close movements of them are controlled by the control system through the actuators. Each cylinder of the engine is equipped with four valves, namely, main and auxiliary intake valves and main and auxiliary exhaust valves, which are independently controlled by electromagnetic actuators in accordance with the engine operation condition, thereby to control the output of the engine.
In addition, for much improving the fuel consumption against the pumping loss of the engine, there has been proposed a measure wherein control of the intake air amount is effected by controlling the close timing (or open period) of each intake valve thereby carrying out the xe2x80x9cnon-throttle operationxe2x80x9d of the engine.
However, even in the above-mentioned measures, it is difficult to obtain a desired operation of the engine at the time when the engine is under high-speed and low-load operation because of the nature of the electromagnetic actuators. That is, the electromagnetic actuators have a limitation in speeding up the actuation to the intake valves. In other words, under high-speed operation of the engine, reduction of load is almost impossible or at least very difficult. That is, for reducing the engine torque, it is necessary to shorten the open period of each intake valve to reduce the intake air amount. This means that the intake valve has to be closed instantly just after its opening movement. However, since the valve actuating speed of the actuator is constant and a certain operation time is needed for closing the intake valve, the minimum open period with respect to the crank angle is not sufficiently small under such high-speed operation. Thus, under such high-speed operation, torque reduction by reducing the intake air amount is substantially impossible.
In view of the above, the applicants have hitherto proposed a measure that is shown Laid-open Japanese Patent Application (viz., Tokkaihei) 2000-45804. In the measure, by controlling open/close cycle of the intake and exhaust valves in accordance with an operation range of the engine, switching is carried out from a normal 4 (four)-cycle operation to a different cycle operation. More specifically, upon the engine assuming a high-speed and low-load condition, switching is carried out from 4-cycle operation to a so-called multi-cycle operation whose cycle is greater than four (4).
For ease of description, such engine operation as allowing switching between different cycle operations will be referred to as xe2x80x9cvariable cycle operationxe2x80x9d in the following.
In view of the above, the present invention aims to provide a control system for controlling a variable valve type internal combustion engine, which suppresses or at least minimizes a torque gap that would occur upon cycle switching between 4-cycle operation and the multi-cycle operation.
With this control, improved fuel consumption due to expansion of the non-throttle operation range and improved driveability due to suppression of the torque gap are both obtained.
According to a first aspect of the present invention, there is provided a control system for controlling a variable valve type internal combustion engine. The engine has cylinders and electromagnetically actuated intake and exhaust valves arranged for each cylinder. The intake air amount fed to the cylinder is controlled by controlling the close timing of the intake valve. The control system comprises an operation range judging section that judges an operation range of the engine; a variable cycle operating section that switches the operation of the engine between 4-cycle operation and a different cycle operation in accordance with the judgment carried out by the operation range judging section, the different cycle operation being of an operation whose cycle is different from the 4-cycle; and an intermediate variable cycle operating section that allows part of the cylinders of the engine to carry out 4-cycle operation and the remaining part of the cylinders to carry out the different cycle operation when the operation range judging section judges that the engine is under an intermediate operation range between an operation range provided by the 4-cycle operation and an operation range provided by the different cycle operation.
According to a second aspect of the present invention, there is provided a control system for controlling a variable valve type internal combustion engine. The engine has cylinders and electromagnetically actuated intake and exhaust valves arranged for each cylinder. The intake air amount fed to the cylinder is controlled by controlling the close timing of the intake valve. The control system comprises means for judging an operation range assumed by the engine; means for switching the operation of the engine between 4-cycle operation and a different cycle operation in accordance with the judgment made by the operation range judging section, the different cycle operation being of an operation whose cycle is different from the 4-cycle; and means for allowing part of the cylinders of the engine to carry out 4-cycle operation and the remaining part of the cylinders to carry out the different cycle operation when the operation range judging section judges that the engine is under an intermediate operation range between an operation range provided by the 4-cycle operation and an operation range provided by the different cycle operation.
According to a third aspect of the present invention, there is provided a method for controlling a variable valve type internal combustion engine. The engine has cylinders and electromagnetically actuated intake and exhaust valves arranged for each cylinder. The intake air amount fed to the cylinder is controlled by controlling the close timing of the intake valve. The method comprises judging an operation range assumed by the engine; switching the operation of the engine between 4-cycle operation and a different cycle operation in accordance with the judgment made by the operation range judging section, the different cycle operation being of an operation whose cycle is different from the 4-cycle; and allowing part of the cylinders of the engine to carry out 4-cycle operation and the remaining part of the cylinders to carry out the different cycle operation when said operation range judging section judges that the engine is under an intermediate operation range between an operation range provided by the 4-cycle operation and an operation range provided by the different cycle operation.
According to a fourth aspect of the present invention, there is provided a control apparatus for a multi-cylinder engine. The control apparatus comprises a first section that operates a four cycle operation when the engine is in a first engine operation range; a second section that operates a different cycle operation when the engine is in a second engine operation range, the different cycle operation being different from the four cycle operation; and a third section that operates an intermediate cycle operation when the engine is in a third engine operation range, the third engine operation range being arranged between the first engine operation range and the second engine operation range, wherein a part of the cylinders are operated on the four-cycle operation and the remaining part of the cylinders are operated on the different cycle operation, in the intermediate cycle operation.